Six people dead after Sydney Seaplane crashes into Hawkesbury River

All six people on board a single-engine sea plane that crashed into Cowan Creek at Jerusalem Bay in Sydney's north on Sunday afternoon have died, police have confirmed.

The Sydney Seaplanes aircraft, carrying a pilot and five passengers, crashed about 3.15pm and a search and rescue operation was attempting to locate the aircraft which is believed to be submerged.

NSW Police confirmed three bodies had been recovered, and an operation was under way to recover the remaining three bodies. There was no further information on the identities of those on board.

Police have recovered three bodies from a sea plane crash, where all six people on board died. Photo: Jessica Hromas

There are unconfirmed reports that those on board were four British Nationals, an 11-year-old boy and the pilot.

The aircraft has not yet been recovered, and police said they were unsure whether it would be able to be recovered on Sunday evening.

The Australian Transport Safety Bureau identified the aircraft as a DHC-2 Beaver Seaplane which was "on a return flight to Rose Bay, Sydney Harbour" from Cottage Point Inn.

A helicopter hovers over the water near where the seaplane is believed to have gone down. Photo: Seven News

"The sequence of events leading up to the accident are not yet understood, however following the impact with the water, the aircraft is reported to have sunk rapidly."

"There are currently no reports of survivors."

Commander of the Kurung-Gai Local Area Command, Acting Superintendent Michael Gorman confirmed all six on board had died.

"We are in the process of recovering the bodies of three other people ... (we will) see if we can recover the plane tonight or whether it will stay in situ tonight until tomorrow morning," acting Supt Gorman told reporters on the scene on Sunday.

Inspector Michael Gorman confirmed that all six on board the sea plane had died. Photo: Jessica Hromas

"We don't know why the plane crashed."

Forensic police are on the way to Cowan Creek where they will try and identify the three bodies that have been recovered.

"(There) certainly were people out on boats and on the water which is why if people have seen what occurred please contact marine area command or crime stoppers," Supt Gorman said.

Debris seen floating in the river where the sea plane went down. Photo: SEVEN NEWS

A spokesman for Sydney Seaplanes confirmed that an incident had occurred with a plane believed to belong to the company.

"We're just working with police to make sure that all assistance can be rendered," the spokesman said.

Seven News reported that phone footage taken by a group of men on a jet ski showed a Sydney Seaplane overhead, believed to have been captured "just moments before it is submerged".